Question

to determine the radius of curvature of a concave mirror using a spherometer.

Answer 1

Aim: To demonstrate the radius of curvature of a concave mirror using a spherometer.
Material Needed: Spherometer, glass strip, concave mirror, plane glass slab, a sheet of paper, a ruler, pencil
Procedure: 1. Raise the screw of spherometer sufficiently upwards.
2. Place the spherometer on the concave mirror so that its three legs rest on it.
3. Gently turn the screw downwards till the screw touches the concave mirror.
4. Note the reading of the circular disc scale which is in line with vertical (pitch)
scale. Note the reading 'a', which will act as reference.
5. Remove the spherometer from over the concave mirror and place it over a long size glass slab.
6.Turn the screw downwards and count the no. of complete rotations made by rotations made by the disc (one rotation becomes complete when the reference reading crosses past the pitch scale.)
7.Continue till the tip of the screw just touches the plane surface of the glass slab.
8. Note the reading of the circular scale which is finally in the line with the vertical (pitch) scale. Note this reading as 'b'.
9.Find the no. of circular (disc) scale division in the last incomplete relation. 
10.Now find total reading using the relation equation 1.
11.Repeat steps 3 to 9, three times. Record the observation in tabular form. 
12. Calculate the radius of curvature of the given concave surface using the equation 2.